Trouble light apparatus are conventionally made with a cage surrounding a lamp secured in a socket with a handle attached having a switch for controlling the applications of power to the socket and thus, the lamp. A conventional cord connects the handle to a plug that is received in a conventional alternating current (ac) (e.g. 120/240 v) receptacle.
It is also known, as shown in U.S. Pat. No. 2,812,423 issued to J. Penna, to employ a 12 volt lamp in a trouble lamp and connect that lamp to a source of 12 v direct current (dc) derived from an automobile's battery. Dual voltage trouble lamp apparatus' are shown in U.S. Pat. Nos. 3,761,862 and 4,310,874, both issued to J. Spiteri. These dual voltage apparatus' operate from either the conventional ac source (120 v ac) or from a low voltage source (e.g. 12 v dc automobile battery), but they require a special dual filament lamp and socket.
It is also known, in another type of light apparatus, to employ a low voltage lamp and alternative power connections. U.S. Pat. No. 4,232,357 to M. S. Dretz. This arrangement is not as "handy" as the conventional trouble lamps.
It is also known to run two lamps (120 v ac and 12 v dc) from a unit attached to a convertible table lamp socket. U.S. Pat. No. 4,638,413.
Despite these approaches, there still exists a need for a dual voltage trouble lamp that employs lower cost, single filament, low voltage lamps and is convenient to change-over from one source to the other.